Abstract Mindfulness meditation and Real-time Brain Activity in Schizophrenia (MARBAIS). Recent work suggests that mindfulness training is effective to treat schizophrenia. In mindfulness training, meditation takes a central position. However, learning to meditate is not straightforward as no immediate feedback to students is possible as there are no easily discernible outward signs of performance. In addition, a teacher's feedback may inadvertently be confounded, due to e.g. the ability of a student to describe internal states, the teacher's ability to interpret the students' verbal descriptions, or the student's interpretation of the teacher's instructions. A possible solution to this issue would be to provide neurofeedback during meditation, so individuals have an unbiased ?mental mirror? which directly informs them on their meditation quality in real time in an unbiased way. In a proof-of-concept study, we showed that EEG neurofeedback from the posterior cingulate cortex (PCC) tracks mindfulness meditation quality in healthy novice meditators. However, as patients with schizophrenia suffer from a broad range of symptoms, including cognitive impairment and reduced attentive capabilities, it is currently unclear whether PCC activity and meditation quality are associated in schizophrenia. In the proposed study, Aim 1 will determine whether EEG neurofeedback from the PCC tracks the subjective experience of mindfulness meditation in schizophrenia. To achieve this, 20 patients with schizophrenia will perform a neurofeedback test-battery while performing mindfulness meditation. Aim 2 will determine whether patients with schizophrenia can volitionally modulate EEG neurofeedback from the PCC using mindfulness meditation. In addition, exploratory aim 3 will investigate whether there is an association between the ability to volitionally modulate neurofeedback from the PCC and schizophrenia- related symptomatology. This would be the first study to assess the association between a neurofeedback signal and meditation quality in schizophrenia. If we find that PCC activity tracks with meditation quality and patients are able to volitionally modulate activity by meditating, it would provide the rationale to investigate the efficacy of this non-pharmacological intervention in a randomized clinical trial.